<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" 
        content="width=device-width, 
        user-scalable=no, 
        initial-scale=1.0, 
        maximum-scale=1.0, 
        minimum-scale=1.0"/>
    <style>  
        html{
            font-size: 1em;
        }
        div{
            font-size: 1.5em;
        }
        p{
            font-size: 1.5em;
        }
        span{
            font-size: 1.5em;
        }
 </style>
<body>
    <div>我是div里的内容
        <p>我是div-->p里面的内容<br/>
            <span>我是div-->p-->span里的内容</span>
        </p>
    </div>
</body>
